Sheet conveying device, sheet punching device, sheet processing device, image forming apparatus, and method for determining mounting state of measuring unit

ABSTRACT

A sheet conveying device includes a conveying unit that conveys a sheet in a sheet conveying direction; a measuring unit that measures a position of a side edge of the sheet in a measurement area; a shielding unit having an end portion that is projected into the measurement area for shielding the sheet; a first determining unit that determines whether the shielding unit is detectable in the measurement area; and a second determining unit that determines whether the measuring unit has been mounted in the sheet conveying device based on a result obtained in the first determining unit.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to and incorporates by referencethe entire contents of Japanese priority document 2008-033423 filed inJapan on Feb. 14, 2008.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a sheet conveying device, a sheetpunching device, a sheet processing device, an image forming apparatus,and a sheet conveying method to be implemented in the sheet conveyingdevice, the sheet processing device, and the image forming apparatus.

2. Description of the Related Art

In a typical sheet post-processing apparatus, a punching unit measures aposition of a side edge of a sheet-like recording medium (hereinafter,“sheet”), and decides a punching position on the sheet based on themeasured position of the side edge. This approach allows accuratesetting of the punching position. Related technologies have beendisclosed in, for example, Japanese Patent No. 3363725 and JapanesePatent Application Laid-open No. 2003-248410.

Japanese Patent No. 3363725 discloses a conventional punching devicethat measures a position of a side edge of a sheet and decides apunching position based on the measured position of the side edge.Specifically, the punching device includes a punching unit that ismovable in a punching direction that is perpendicular to a sheetconveying direction and can punch a conveyed sheet at a desiredposition; a detecting unit that detects a side edge of a sheet conveyedto the punching unit in the sheet conveying direction; and a moving unitthat moves the punching unit in the punching direction based on theposition of the side edge detected by the detecting unit. In particular,the detecting unit is moved in advance to a position near the side edgeof the conveyed sheet based on information about a size of the sheet.

However, with the current increase in the sheet conveying speed and theprinting speed, the time available for moving the detecting unit to theside edge of the conveyed sheet is becoming shorter and shorter.Therefore, it is technically difficult to move the detecting unit inpunching units with fast processing speed. To take care of this issue, acontact image sensor (CIS) is now a days used in image formingapparatuses for measuring a position of the side edge of a conveyedsheet. For example, Japanese Patent Application Laid-open No.2003-248410 discloses a conventional technology in which a CIS is usedto detect a side edge of a conveyed sheet. Specifically, the CIS isarranged in a sheet-conveying area such that reading pixels of the CISare aligned in a direction substantially perpendicular to a sheetconveying direction. One-seventh of the total reading pixels arerepeatedly read in a shorter period (TS) to detect a leading end of aconveyed sheet. After a predetermined waiting time has elapses from atiming of detection of the leading end of the sheet, image writing in asub-scanning direction is started by irradiating a laser onto aphotosensitive element. Meanwhile, six-seventh of the total readingpixels are read in a longer period to detect a lateral position of theconveyed sheet. A misregistration amount is calculated based on thedetected lateral position, and a writing position in a main-scanningdirection on the sheet is corrected based on the misregistration amount.

In this manner, a processing speed for detecting a side edge of a sheetcan be improved by using the CIS. However, such an advantage can beachieved only when the CIS is mounted properly with good precision.Therefore, it is necessary to check, after mounting the CIS, whether theCIS has been mounted properly. One method of checking whether the CIS ismounted properly is as follows. That is, a sheet is set in an offsetmanner in a sheet feeding unit of an image forming apparatus, and animage is formed on the sheet on a trial basis to see whetherimage-misalignment occurs.

The above technique can be used if a CIS is mounted in an image formingapparatus right from the beginning, i.e., during assembly of the imageforming apparatus. However, a CIS can be provided in a punching unit ofa sheet post-processing apparatus, i.e., at a later stage of assembly ofthe image forming apparatus, for improvement of the accuracy of thepunching position. Because a punching unit is often an optional deviceto be installed depending on a request from users, the punching unit isgenerally set and checked by a field service person at a customerlocation, so that assembly error or checking failure is likely to occur.The accuracy of the punching position also depends on how a sheet isconveyed. For example, if a sheet is conveyed without skew or lateralmisregistration, the accuracy of the punching position will be better.Therefore, whether a CIS is operating normally, or a CIS has beenmounted at all, cannot always be checked by printing an image on a sheeton a trial basis as in the above technique. In other words, the abovetechnique is not always effective to determine whether a measuring unitfor measuring a position of a side edge of a sheet is operatingnormally, or whether the measuring unit has been mounted at all in theapparatus.

SUMMARY OF THE INVENTION

It is an object of the present invention to at least partially solve theproblems in the conventional technology.

According to an aspect of the present invention, there is provided asheet conveying device including a conveying unit that conveys a sheetin a sheet conveying direction; a measuring unit that measures aposition of a side edge of the sheet in a measurement area; a shieldingunit having an end portion that is projected into the measurement areafor shielding the sheet; a first determining unit that determineswhether the shielding unit is detectable in the measurement area; and asecond determining unit that determines whether the measuring unit hasbeen mounted in the sheet conveying device based on a result obtained inthe first determining unit.

According to another aspect of the present invention, there is provideda method for determining whether a measuring unit is mounted in a sheetconveying device that includes a conveying unit that conveys a sheet ina sheet conveying direction; a measuring unit that measures a positionof a side edge of the sheet in a measurement area; and a shielding unithaving an end portion that is projected into the measurement area forshielding the sheet. The method includes first determining includingdetermining whether the shielding unit is detectable in the measurementarea; and second determining including determining whether the measuringunit is mounted based on a result obtained at the first determining.

The above and other objects, features, advantages and technical andindustrial significance of this invention will be better understood byreading the following detailed description of presently preferredembodiments of the invention, when considered in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a printing system including a sheetpost-processing apparatus and an image forming apparatus according to anembodiment of the present invention;

FIG. 2 is a schematic diagram of a lateral-registration detecting unitand a punching unit according to the embodiment;

FIG. 3 is a schematic diagram illustrating a positional relation betweena contact image sensor (CIS) and a shielding plate according to theembodiment;

FIG. 4 is a schematic diagram of the punching unit shown in FIG. 2;

FIG. 5 is a block diagram of an electrical configuration of the printingsystem shown in FIG. 1;

FIG. 6 is a diagram illustrating a relation between detection of aleading end of a sheet by an entrance sensor and driving of entrance(conveying) rollers when skew correction is performed;

FIG. 7 is a flowchart of a control process for driving the entrancerollers;

FIG. 8 is a schematic diagram for explaining a measurement start timingof the CIS with respect to a sheet;

FIG. 9 is a schematic diagram illustrating a positional relation amongthe lateral-registration detecting unit that includes a CIS, thepunching unit, and a conveyed sheet;

FIG. 10 is a schematic diagram for explaining detection of a sheet bythe CIS;

FIG. 11 is a block diagram of a lateral-misregistration detectioncircuit that detects lateral misregistration of a sheet;

FIG. 12 is a schematic diagram illustrating reference conveyingpositions of sheets of various sizes;

FIG. 13 is a schematic diagram for explaining detection of the shieldingplate by the CIS in the situation shown in FIG. 12;

FIG. 14 is a flowchart of a control process for detecting the shieldingplate in the situation shown in FIG. 13;

FIG. 15 is a schematic diagram illustrating a positional relation amongthe CIS, a conveyed sheet, and the shielding plate;

FIG. 16 is a side view of the CIS, the conveyed sheet, and the shieldingplate in the situation shown in FIG. 15;

FIG. 17 is a schematic diagram for explaining detection of the sheet bythe CIS in the situation shown in FIGS. 15 and 16; and

FIG. 18 is a schematic diagram for explaining detection of the sheet andthe shielding plate by the CIS where the shielding plate is arranged onthe side opposite to the side of a center line of a sheet in a sheetconveying direction.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Exemplary embodiments of the present invention are explained in detailbelow with reference to the accompanying drawings.

In the following embodiments, a conveying unit corresponds to conveying(entrance) rollers 1, a measuring unit corresponds to a lateralregistration sensor 414 and a contact image sensor (CIS) 201, ameasurement area corresponds to a reading range (measurement area) R, ashielding unit corresponds to a shielding plate 202, a determining unitcorresponds to a CPU 111, and an operation panel corresponds to anoperation panel 113.

FIG. 1 is a schematic diagram of a printing system including a sheetpost-processing apparatus PD as a sheet finisher and an image formingapparatus PR according to an embodiment of the present invention. InFIG. 1, the entire configuration of the sheet post-processing apparatusPD and only a part of the image forming apparatus PR are shown.

The sheet post-processing apparatus PD is coupled to the image formingapparatus PR, and receives a recording medium, such as a sheet, from theimage forming apparatus PR. The sheet then passes through a conveyingpath including a post processing unit (in the embodiment, a punchingdevice 100) that performs post processing on the sheet. Then, the sheetis conveyed to any one of a conveying path for guiding the sheet to anupper tray 501, a conveying path for guiding the sheet to a shift tray502, and a conveying path for guiding the sheet to a processing tray F(hereinafter, referred to as “staple processing tray F”) that performsaligning and stapling, by a branching claw 15 and a branching claw 16.

Sheets that are guided by the branching claws 15 and 16 to the stapleprocessing tray F where the sheets are aligned and stapled are thenconveyed as a stapled sheet stack to either a conveying path for guidingthe sheets to the shift tray 502 or a processing tray G (hereinafter,referred to as “center-folding tray G”) for folding the stapled sheetstack, by a branching guide plate 54 and a movable guide 55 thatfunction as a deflecting unit. The stapled sheet stack that iscenter-folded in the center-folding tray G is guided to a lower tray 503via a sheet discharging path. A branching claw 17 is arranged in aconveying path from the branching claw 16 to the staple processing trayF. The branching claw 17 is maintained in the state shown in FIG. 1 by alow-load spring (not shown). After a trailing end of a sheet conveyed bya pair of conveying rollers 7 passes the branching claw 17, the sheet isconveyed backward with a pair of prestack rollers 8 due to reverserotation of at least a pair of conveying rollers 9 out of the conveyingrollers 9, a pair of conveying rollers 10, and a pair of staple sheetdischarge rollers 11 so that the trailing end of the sheet is guided toand temporarily held in a sheet storage unit E. When a next sheet isconveyed, the next sheet is stacked on the preceding sheet andtemporarily held in the sheet storage unit E in the same manner. In thismanner, a stack of sheets to be stapled is prepared inside the sheetstorage unit E and finally conveyed to the staple processing tray F. Itis also possible to stack and convey three or more sheets in anoverlapped manner by repeating the above operation. A sheet sensor 304is arranged on the upstream side of the conveying rollers 9 in a sheetconveying direction and a sheet detection sensor 305 is arranged on thedownstream side of the conveying rollers 10 in the sheet conveyingdirection for detecting the trailing end of the sheet.

An entrance sensor 301 detects entry of a sheet in the sheetpost-processing apparatus PD from the image forming apparatus PR. A pairof entrance (conveying) rollers 1, the punching device 100, a pair ofconveying rollers 2, the branching claw 15, and the branching claw 16are arranged in that order on the downstream side of the entrance sensor301. The branching claws 15 and 16 are maintained in the state shown inFIG. 1 by springs (not shown). When solenoids (not shown) are turned on,the branching claw 15 rotates upward and the branching claw 16 rotatesdownward so that sheets can be guided to each of the above-mentionedconveying paths. A hopper 101 is arranged below the punching device 100for collecting punching waste (dust). The hopper 101 can be removed outof the sheet post-processing apparatus PD from a door (not shown)arranged on the front side of the sheet post-processing apparatus PD, sothat punching waste collected in the hopper 101 can be discarded asappropriate. The hopper 101 is provided with a full-state sensor (notshown) for detecting whether the hopper 101 is full of punching waste.

When guiding a sheet to the upper tray 501, the solenoid for thebranching claw 15 is turned off to keep the state shown in FIG. 1. Whenguiding a sheet to a conveying path C, the solenoids for the branchingclaws 15 and 16 are turned on while the branching claws 15 and 16 are inthe state shown in FIG. 1, so that the branching claw 15 rotatesdownward. As a result, the sheet is discharged onto the upper tray 501through a pair of conveying rollers 3, a pair of conveying rollers 4,and a pair of upper discharge rollers 5. The state of a sheet beingdischarged is detected by an upper discharge sensor 302. When guiding asheet to the staple processing tray F, the solenoid for the branchingclaw 16 is turned off to keep the state shown in FIG. 1 and the solenoidfor the branching claw 15 is turned off while the branching claw 15 isin the state shown in FIG. 1, so that the branching claw 15 rotatesupward.

The sheet post-processing apparatus PD is capable of performing variouskinds of processing on sheets such as punching (using the punchingdevice 100), aligning and side-stitching, i.e., stapling anside-stitching (using a jogger fence 53 and an side-stitching staplerS1), aligning and saddle stitching (using the jogger fence 53 and asaddle-stitching stapler S2), sorting (using the shift tray 502), andcenter folding (using a folding plate 74 and a pair of folding rollers81).

A shift-tray sheet discharge unit for discharging sheets onto the shifttray 502 includes a pair of shift sheet discharge rollers 6, a returnroller 13, a sheet surface sensor 330, the shift tray 502, a shiftmechanism (not shown), and shift-tray lifting mechanism (not shown). Oneof the shift sheet discharge rollers 6 serves as a driving roller 6 aand the other serves as a driven roller 6 b. The driven roller 6 b isattached to a free end of an open-close guide plate. The open-closeguide plate is rotatable around a fulcrum that is the other end locatedon the upstream side in the sheet conveying direction. The driven roller6 b comes into contact with the driving roller 6 a by gravity or abiasing force, so that a sheet being discharged is nipped between thedriving roller 6 a and the driven roller 6 b. If a stapled sheet stackis discharged, the open-close guide plate is lifted upward and thendownward to a stop position at a predetermined timing. The predeterminedtiming is determined based on a detection signal from a shift sheetdischarge sensor 303. The stop position is determined based on adetection signal from a discharging-guide-plate open-close sensor (notshown). The guide plate is driven by a discharging-guide-plateopen-close motor (not shown).

The staple processing tray F that performs staple processing isconfigured and operates as follows. That is, sheets discharged by thestaple sheet discharge rollers 11 are sequentially stacked on the stapleprocessing tray F. Every time a sheet is stacked on the stapleprocessing tray F, the sheet is aligned in a longitudinal direction (asheet conveying direction) by a tapping roller 12 and aligned in alateral direction (a direction perpendicular to the sheet conveyingdirection, i.e., a sheet width direction) by the jogger fence 53. Theside-stitching stapler S1 is driven to perform side-stitching inresponse to a stapling signal from a control device during the timebetween jobs, i.e., between the time when the last sheet of the presentsheet stack is received and the time when the first sheet of the nextsheet stack is received. Immediately thereafter, the side-stitchingstapled sheet stack is conveyed to the shift sheet discharge rollers 6by a discharge belt 52, from which discharge claws 52 a are projected,and is discharged onto the shift tray 502 set at a position forreceiving the sheet stack.

A home position of the discharge claw 52 a is detected by adischarge-belt HP sensor 311. The discharge-belt HP sensor 311 is turnedon and off by the discharge claw 52 a. In the embodiment, the twodischarge claws 52 a are arranged on the outer circumferential surfaceof the discharge belt 52 at oppositely spaced positions, and alternatelyconvey a sheet stack out of the staple processing tray F. The leadingend of a sheet stack in the staple processing tray F can be aligned byusing a front end of the discharge claw 52 a through which the sheetstack is to be conveyed and a rear end of the other discharge claw 52 aby reversely rotating the discharge belt 52. In other words, thedischarge claws 52 a also serve as an aligning unit for aligning a sheetstack in the sheet conveying direction.

The discharge belt 52 and a drive pulley are arranged on a drive shaftof the discharge belt 52 that is driven by a discharge motor (notshown), along a center line of a sheet in a sheet width direction. Aplurality of discharge rollers 56 is arranged and fixed symmetricallywith respect to the drive pulley. The circumferential speed of thedischarge rollers 56 is set to be higher than that of the discharge belt52. The tapping roller 12 rotates around a fulcrum by a tapping solenoid(SOL). The tapping roller 12 intermittently taps a sheet fed into thestaple processing tray F to bring the sheet into contact with a trailingend fence 51. The tapping roller 12 rotates counterclockwise. The joggerfence 53 is driven by a jogger motor (not shown) capable of rotatingreversely via a timing belt and reciprocates in the sheet widthdirection.

The side-stitching stapler S1 is driven by a stapler-moving motor (notshown) that can run reversely via the timing belt (not shown). Theside-stitching stapler S1 is moved in the sheet width direction tostaple a sheet stack at a predetermined end position. A stapler-movingHP sensor that detects a home position of the side-stitching stapler S1is arranged on one end of a movable range of the side-stitching staplerS1. A stapling position of the sheet stack in the sheet width directionis controlled based on the moving amount of the side-stitching staplerS1 from the home position. The saddle-stitching stapler S2 is arrangedsuch that the distance from the trailing end fence 51 to a staplingposition by the saddle-stitching stapler S2 is equal to or longer thanhalf of the length of a sheet of the maximum size that can besaddle-stitched. Furthermore, two saddle-stitching staplers S2 arearranged symmetrically with respect to the center line of a sheet in asheet width direction and fixed to a stay. The saddle-stitching staplerS2 has a known configuration and therefore detailed explanation isomitted. When performing saddle stitching, the jogger fence 53 alignsthe sheets in a direction perpendicular to the sheet conveyingdirection, and the trailing end fence 51 and the tapping roller 12 alignthe sheets in the sheet conveying direction. Thereafter, the dischargebelt 52 is driven to lift a stack of the sheets while the discharge claw52 a supports the trailing end of the sheet stack until the center ofthe sheet stack is positioned to the stapling position by thesaddle-stitching staplers S2. Then, the discharge belt 52 is stopped andthe sheet stack is saddle-stitched by the saddle-stitching staplers S2.The saddle-stitched sheet stack is conveyed to the center-folding tray Gto be center-folded. In FIG. 1, reference numeral 310 is a sheet sensorthat detects a sheet on the staple processing tray F.

The sheet stack that is stapled in the staple processing tray F iscenter-folded at the center of the sheet stack in the center-foldingtray G. To perform center folding, the stapled sheet stack needs to beconveyed to the center-folding tray G. In the embodiment, a sheet stackdeviation unit is provided on the most downstream side of the stapleprocessing tray F in the sheet conveying direction so that thesaddle-stitched sheet stack is conveyed from the staple processing trayF to the center-folding tray G for center folding. The sheet stackdeviation unit includes the branching guide plate 54 and the movableguide 55. The branching guide plate 54 is provided to be swingablearound a fulcrum upwardly and downwardly, and a rotatable pressingroller 57 is provided on the downstream side of the branching guideplate 54. The branching guide plate 54 is pressed toward the dischargerollers 56 by a spring (not shown). The position of the branching guideplate 54 is determined based on a contact position between the branchingguide plate 54 and the surface of a cam (not shown) that is driven torotate by a sheet-stack branching motor (not shown). The movable guide55 is swingably supported by the rotation shaft of the discharge rollers56 such that one end of the movable guide 55 (on the side opposite tothe branching guide plate 54) is driven and a stop position is set by alink arm (not shown) that is rotatably connected to a connecting unit(not shown).

The center-folding tray G includes an upper sheet-stack guide plate 92,a lower sheet-stack guide plate 91, a pair of upper sheet-stackconveying rollers 71, a pair of lower sheet-stack conveying rollers 72,the folding rollers 81, a sheet-discharging path, a lower dischargeroller 83, the folding plate 74, a movable trailing end fence 73, alifting mechanism, a sheet-stack arrival sensor 321, an HP sensor 322,and a folding-unit passage sensor 323.

The upper sheet-stack guide plate 92 and the lower sheet-stack guideplate 91 are arranged in a direction substantially perpendicular to theouter circumference of the movable guide 55 mounted on the dischargerollers 56. The upper sheet-stack conveying rollers 71 and the lowersheet-stack conveying rollers 72 are arranged on the upper sheet-stackguide plate 92. The folding rollers 81 are arranged on the adjacentportion of the upper sheet-stack guide plate 92 and the lowersheet-stack guide plate 91. The sheet-discharging path is extended froma nip of the folding rollers 81 in a horizontal direction. The foldingplate 74 reciprocates in a horizontal direction with respect to the nipof the folding rollers 81 so that a sheet stack is folded and tuckedinto the nip of the folding rollers 81. The movable trailing end fence73 is projected from the lower sheet-stack guide plate 91. The liftingmechanism lifts the movable trailing end fence 73 up and down. Thesheet-stack arrival sensor 321 is arranged at a position on thedownstream side of the lower sheet-stack conveying rollers 72 and theupstream side of a position where a sheet stack is to be folded. The HPsensor 322 is provided for detecting a home position of the movabletrailing end fence 73. The folding-unit passage sensor 323 is providedfor detecting a sheet stack passing through the sheet-discharging path.

In the embodiment, it is assumed that a sheet stack is center-folded.However, center-folding can be applied to one sheet instead of a sheetstack. In this case, a sheet is directly conveyed to the center-foldingtray G after being discharged because saddle-stitching is not necessary.The sheet conveyed to the center-folding tray G is center-folded by thefolding plate 74 and the folding rollers 81, and then discharged on thelower tray 503.

As shown in FIG. 2, the punching device 100 includes alateral-registration detecting unit A and a punching unit B, FIG. 3 is aschematic diagram illustrating a positional relation between the CIS 201and the shielding plate 202, and FIG. 4 is a side view of the punchingunit B.

The punching unit B includes a punching blade 415, a holder 437integrally arranged on an upper end portion of the punching blade 415, acam 438 inserted into the holder 437 and eccentrically engaged with ashaft 416, a motor 418 that drives the punching blade 415, a secondstepping motor 423 that moves the punching blade 415 in a directionperpendicular to the sheet conveying direction, a timing belt 424, agear/pulley 436, a rack 419, an upper guide plate 433, a lower guideplate 435, and a paper sensor 402. A punching-waste guide 405 isarranged below the punching blade 415. This punching-waste guide 405guides punching waste to the hopper 101. Reference numeral 420 denotesan upper punching guide and reference numeral 421 denotes a lowerpunching guide.

In the sheet post-processing apparatus PD configured as described above,a leading end of a sheet fed from the image forming apparatus PR isbrought into contact with a nip of the entrance rollers 1 (hereinafter,referred to as “skew-correction rollers 1” as appropriate) that are notrotating. The sheet is continuously pressed towards the nip for apredetermined time until the sheet is bent by an adequate amount.Thereafter, the skew-correction rollers 1 are driven to rotate, wherebythe sheet is conveyed. A stop time and a rotation start timing of theskew-correction rollers 1 are determined based on detection of aleading-end of the sheet by the entrance sensor 301 as a trigger. Thesheet that has been aligned due to skew correction by theskew-correction rollers 1 first enters the lateral-registrationdetecting unit A and then enters the punching unit B.

The lateral-registration detecting unit A includes the CIS 201 as asheet-end measuring unit that detects a position of a side edge, or alateral end, of a sheet conveyed to the lateral-registration detectingunit A. The side edge, or the lateral end, of a sheet is a side of thesheet that is parallel to the sheet conveying direction. The CIS 201 isarranged on a sheet guide (not shown) such that a reading line directionof the CIS 201 becomes perpendicular to the sheet conveying direction.In the embodiment, the CIS 201 is used as the sheet-end-positionmeasuring unit. However, a line sensor, or a charge coupled device (CCD)sensor, can be used instead of the CIS 201.

The second stepping motor 423 serves as a driving source of the punchingunit B, and rotates the gear/pulley 436 by applying a driving force viathe timing belt 424. A gear provided in the gear/pulley 436 is engagedwith the rack 419, so that the rack 419 moves in directions indicated byarrows X in FIG. 4 due to rotation of the gear/pulley 436. The rack 419is mounted on the lower punching guide 421. The components that punch asheet (the punching blade 415, the upper punching guide 420, the shaft416, the cam 438, the holder 437, a clutch 417, and the motor 418) areconnected to the lower punching guide 421. Therefore, the abovecomponents are moved in a direction (the direction indicated by thearrows X in FIG. 4) perpendicular to the sheet conveying direction bymoving the rack 419.

As shown in FIG. 5, the control unit 110 is a microcomputer thatincludes the CPU 111, an input-output (I/O) interface 112, and the like.The CPU 111 receives various signals via the I/O interface 112 fromvarious devices such as switches on the operation panel 113 of the imageforming apparatus PR, the upper discharge sensor 302 for detecting thestate of a sheet being discharged on the upper tray 501, the shift sheetdischarge sensor 303 for detecting the state of a sheet being dischargedon the shift tray 502, the folding-unit passage sensor 323 for detectingthe state of a sheet being discharged on the lower tray 503, and thesheet surface sensor 330 for detecting a height of a sheet surfacestacked on the shift tray 502. The CPU 111 controls the followingcomponents based on the input signals. That is, the punching blade 415is caused to move upward and downward; the jogger fence 53 is caused tomove in a direction perpendicular to the sheet conveying direction; theside-stitching stapler S1 and the saddle-stitching stapler S2 are causedto perform stapling, the stapled sheet stack is caused to be discharged;the shift tray 502 is caused to move upwardly and downwardly; thetapping roller 12 is caused to tap a sheet towards the trailing endfence 51 so that the sheet is aligned in the sheet conveying direction;and the rollers 1 to 7, and 9 to 11 are caused to rotate. With the abovecontrol, the CPU 111 measures a position of a side edge of a sheet basedon output from the CIS 201.

The sheet post-processing apparatus PD is controlled with theabove-mentioned control in the following manner. That is, the CPU 111loads a computer program written in a read only memory (ROM) (not shown)onto a random access memory (RAM) (not shown), and executes the computerprogram while storing necessary data into the RAM. Computer program datacan be stored in a server or other recording media such that thecomputer program data can be downloaded and updated via a network or arecording-media driving device. It is applicable to have integratedconfigurations by, for example, incorporating the sheet post-processingapparatus PD in the image forming apparatus PR.

A sheet that has been processed by the image forming apparatus PR isconveyed to the punching device 100. At this time, the sheet often getsshifted (skewed) from a designated position, and such skew needs to becorrected to improve the accuracy of punching positions. Therefore, whena sheet is to be punched, the sheet is brought into contact with a nipbetween the entrance rollers 1 that are not rotating, so that a leadingend of the sheet is aligned by the nip position and the skew iscorrected.

FIG. 6 is a diagram illustrating a relation between detection of aleading end of a sheet by the entrance sensor 301 and driving of theentrance rollers 1 when skew correction is performed. A leading end of asheet conveyed from the image forming apparatus PR makes a contact withthe entrance rollers 1. In this situation, the entrance sensor 301detects the sheet, i.e., the entrance sensor 301 is turned on. The sheetis then continuously pushed towards the nip for a predetermined time(from a timing TM0 to a timing TM1) until the sheet is bent by anadequate amount. Thereafter, the entrance rollers 1 are driven to anaccelerated speed (from the timing TM1 to a timing TM2) that is fasterthan a reception speed, and continuously driven at the accelerated speedfor a predetermined time (from the timing TM2 to a timing TM3)corresponding to the preset amount. When the sheet, which was bent, isflattened, the entrance rollers 1 are decelerated to the reception speed(from the timing TM3 to a timing TM4). Then, the entrance rollers 1continuously rotate at the reception speed (the timing TM4 or later),whereby the sheet is conveyed. A stop time and a rotation start timingof the entrance rollers 1 are determined based on leading-end detectionby the entrance sensor 301 as a trigger.

FIG. 7 is a flowchart of a control process for driving the entrancerollers 1 when the entrance sensor 301 detects leading end of a sheet.

When a sheet is discharged out of the image forming apparatus PR (YES atStep S101) and the entrance sensor 301 is turned on (YES at Step S102),a counter T1 is reset and then restarted (Step S103). After apredetermined time (from the timing TM0 to the timing TM1) elapses (YESat Step S104), the entrance rollers 1 are accelerated to the acceleratedspeed (from the timing TM1 to the timing TM2: Step S105). When theacceleration is completed (at the timing TM2: YES at Step S106), thecounter T1 is reset and restarted (Step S107). After a predeterminedtime (from the timing TM2 to the timing TM3) elapses (YES at Step S108),the entrance rollers 1 are decelerated to the reception speed (at thetiming TM3: Step S109). As a result, skew of a sheet can be corrected bythe entrance rollers 1.

The CIS 201 that functions as a measuring unit for measuring a positionof a lateral end of a sheet acquires positional data about a lateralregistration of a sheet that has been aligned by skew correction. FIG. 8is a schematic diagram for explaining a measurement start timing of theCIS 201 with respect to a sheet. The measurement start position ispreferably corresponding to a side edge of a punching hole Pa shown inFIG. 8 in a main-scanning direction so that effects due to skew can beremoved as much as possible. The measurement start timing can becalculated by a timer using an ON signal (detection of a leading end ofa sheet) or an OFF signal (detection of a trailing end of a sheet) fromthe entrance sensor 301, or by using pulse counts when the entrancerollers 1 is provided with a stepping motor as a driving source.

FIG. 9 is a schematic diagram illustrating a positional relation amongthe lateral-registration detecting unit A including the CIS 201, thepunching unit B, and a conveyed sheet. The punching unit B is capable ofmoving in a direction (a moving direction indicated by an arrow in FIG.9) perpendicular to the sheet conveying direction by the second steppingmotor 423 as described above. The punching unit B controls its stopposition based on a position of a conveyed sheet, so that a punchingposition can be accurately determined. The CIS 201 detects a distance Lto the side edge of the sheet. The misregistration amount x is obtainedas a difference between a designated (ideal) distance M and the measureddistance L. Assuming that the designated distance M, i.e., the distancefrom a home position to a designated position, is 7.5 millimeters, thepunching unit B moves by a distance obtained by subtracting xmillimeters from 7.5 millimeters. As a result, the sheet can be punchedat a correct position.

FIG. 10 is a schematic diagram for explaining detection of a sheet bythe CIS 201. When the CIS 201 receives a clock (CLK) and a triggersignal (TG), it starts operating. After a predetermined number of theclocks (r in FIG. 10) are received, an output from the CIS 201 isperformed per one pixel by one clock from the first pixel. The higher isthe reflectivity of the sheet, the higher will be the output level of asensor output from the CIS 201. Therefore, when an analog sensor outputfrom the CIS 201 is binarized by use of an appropriate threshold level(a binarization threshold (TH) in FIG. 10), the analog sensor output canbe digitalized as a sheet “exists” or “absent”. In an example shown inFIG. 10, because the sensor output of the CIS 201 is low at all timepoints from (TMa) to (TMb), the binarized output will have a low logicallevel, and after the time point TMb, where the sheet exists, because thesensor output is higher than the threshold level, the binarized outputwill have a high logical level. In detecting a sheet position, thenumber of the clocks from the trigger signal (TG) until the binarizationoutput becomes high level (TMb) in FIG. 10) are counted, or a time fromthe trigger signal (TG) until the binarization output attains a highlogical level is measured, i.e., distance (time) P in FIG. 10 ismeasured.

The position of the sheet is obtained from the first pixel (TMb) in FIG.10) of the CIS 201 as the lateral registration sensor 414 by using thefollowing Equation:L=P−r   (1)where L corresponds to L indicated in FIG. 9. Accordingly, themisregistration amount is obtained by use of “M−L”. Here, P is ameasured value while r is a fixed known value.

FIG. 11 is a block diagram of a circuit configuration of alateral-misregistration detection circuit for detecting lateralmisregistration of a sheet. The CPU 111 is a one-chip CPU and controlsthe sheet post-processing apparatus PD. Specifically, the CPU 111 (a)causes a light emitting diode (LED) driver 121 to output a controlsignal to the CIS 201, (b) outputs a trigger signal TG for a measurementstart to the CIS 201, and (c) causes an oscillating circuit 122 tooutput a clock to the CIS 201.

Then, (d) an analog output from the CIS 201 is digitalized by abinarization circuit 124 and input to a sheet-end position measuringunit 125. The sheet-end position measuring unit 125 measures the numberof the clocks (CLK) until the digitalized signal output from thebinarization circuit 124 indicates a high logical level that correspondsto a sheet end, thereby measuring the sheet position. Subsequently, (e)the measured sheet position is input to a data-error determining unit126. When the measured sheet position deviates from a theoretical sheetposition determined from the sheet size, or the sheet end cannot bedetected at all, the data-error determining unit 126 determines that anerror has occurred. When an error has occurred, (f) the data-errordetermining unit 126 inputs an abnormal signal (1 at the abnormal time)to each gate circuit, the CPU 111, and an error-value generationcounting unit 123.

The error-value generation counting unit 123 counts how many times anerror signal has been output from the data-error determining unit 126and (g) outputs the count to the CPU 111. Then, (g) the CPU 111 outputsa counter-clear signal to reset the count in the error-value generationcounting unit 123. (e) A storage unit 128 stores therein the measuredsheet position output from the sheet-end position measuring unit 125 viaa gate circuit 132 when a normal signal (0 at the normal time) is outputfrom the data-error determining unit 126.

When storing the measured sheet position in the storage unit 128, themeasured sheet position can be stored with respect to each sheet size,or can be classified into groups depending on job content. When (m) theCPU 111 outputs a start/setting signal to an average calculating unit131, (i) an integrating unit 130 integrates data sent from the storageunit 128 and (j) sends integrated data to the average calculating unit131. (k) The average calculating unit 131 then calculates an average. Amisregistration calculating unit 127 calculates a misregistration amountof a sheet end. When the measured sheet position is normal, thesheet-end position measuring unit 125 inputs the measured sheet positionto the misregistration calculating unit 127 via a gate circuit 133. Whenthe measured sheet position is abnormal, (n) data selected by a dataselecting unit 129 based on a selection signal from the CPU 111 is inputto the misregistration calculating unit 127. (p) The misregistrationcalculating unit 127 calculates a misregistration amount of a sheet end,and then, and supplies the misregistration amount to the CPU 111. TheCPU 111 drives the second stepping motor 423 by the amount correspondingto the misregistration amount to move the punching unit B to a correctposition.

Returning to the explanation of FIG. 3, the shielding plate 202 as ashielding unit is arranged in a measurement area of the sheet-endposition measuring unit 125. In other words, a projected end portion ofthe shielding plate 202 is arranged within a reading range (measurementarea) R of the CIS 201. The shielding unit is not limited to theshielding plate 202. FIG. 12 is a schematic diagram illustratingreference conveying positions of sheets of various sizes. The shieldingplate 202 shields an optical path from the CIS 201 to a reading objectso that the CIS 201 reads a surface of the shielding plate 202 insteadof the reading object. The reading range (measurement area) Rcorresponds to a range from the first pixel to the last pixel to be readby the CIS 201.

A sheet fed from the image forming apparatus PR is conveyed to one ofthe positions shown in FIG. 12, which are ideal layout positions,depending on the size of the sheet. However, skew or lateralmisregistration usually occurs on the conveyed sheet. The skew and thelateral misregistration are corrected in the manner as described above.

The shielding plate 202 is arranged at a position closer to a centerline of a sheet in the sheet conveying direction than a position of theside edge of a sheet of the minimum correctable size (in the embodiment,B5 portrait). It is necessary to consider a distance of lateralmisregistration that can be corrected, an assembly error of the CIS 201,and an assembly error of the shielding plate 202 when assembling theshielding plate 202. With this arrangement, the shielding plate 202 canbe assuredly detected by using binarized data obtained by the CIS 201.In an example shown in FIG. 12, a portion of the CIS 201 shielded by theshielding plate 202 is a detection portion 201 a by which the shieldingplate 202 is detected, and the rest of the CIS 201 is a non-detectionportion 201 b.

FIG. 13 is a schematic diagram for explaining detection of the shieldingplate 202 by the CIS 201. The shielding plate 202 can be detected basedon a calculated value L shown in FIG. 13. A positional relation betweenthe CIS 201 and the shielding plate 202 is known from the mechanicallayout. Therefore, the position of the shielding plate 202 can berepresented by a parameter k in FIG. 13, where k corresponds to adistance from an end portion of the shielding plate 202 to an endportion of elements (photodetecting elements) of the CIS 201.

Whether the shielding plate 202 is detected can be determined by thefollowing Inequality:k−α≦Q−L≦k+α  (2)where α represents an assembly error in the mechanical layout, Q is aparameter representing a readable length of the CIS 201, and Lrepresents the calculated value. If Inequality (2) is satisfied, it isdetermined that the shielding plate 202 has been detected. If mountingfailure of a connector of the CIS 201 occurs, or if the CIS 201 isbroken, the sensor output from the CIS 201 becomes zero (Q−L=0).Therefore, Inequality (2) is not satisfied. In this case, it isdetermined that the shielding plate 202 has not been detected, whichindicates an abnormal state.

FIG. 14 is a flowchart of a control process for detecting the shieldingplate 202.

When detecting the shielding plate 202, the lateral registration sensor414 performs reading control to acquire the values L, P, Q, k, and r asdescribed above in connection with FIG. 13 (Step S201). In theembodiment, the CIS 201 that is employed as the lateral registrationsensor 414 performs the reading control. Whether Inequality (2) issatisfied is determined based on the acquired values (step S202). IfInequality (2) is satisfied (YES at Step S202), it is determined thatthe CIS 201 is operating normally (Step S203). If Inequality (2) is notsatisfied (NO at Step S202), it is determined that the CIS 201 is notoperating normally, or that the CIS 201 is not mounted at all (StepS204).

FIG. 15 is a schematic diagram illustrating a positional relation amongthe CIS 201, a conveyed sheet, and the shielding plate 202. FIG. 16 is aside view of the conveyed sheet, the CIS 201, and the shielding plate202 in the situation shown in FIG. 15. FIG. 17 is a schematic diagramfor explaining detection of the sheet by the CIS 201 in the situationshown in FIGS. 15 and 16. As described above, the shielding plate 202 isarranged at a position closer to the center line of the sheet in thesheet conveying direction than a side edge of a sheet of the minimumsize that is available for skew correction. Therefore, as shown in FIG.17, the binarized output from the side edge of a sheet to the centerline of the sheet in the sheet conveying direction is at a high logicallevel regardless of whether the shielding plate 202 is provided. In thiscase, the side edge of the sheet can always be detected.

Assuming that the shielding plate 202 is arranged on the side oppositeto the side of the center line of the sheet in the sheet conveyingdirection, an end portion of the shielding plate 202 is at a positioncloser to the center line of the sheet in the sheet conveying directionthan the first pixel of the CIS 201. FIG. 18 is a schematic diagram forexplaining detection of the sheet and the shielding plate 202 by the CIS201 in the above situation. As shown in FIG. 18, both the shieldingplate 202 and the sheet are detected due to binarization. At this state,even when the value P from the trigger signal until a binarizationoutput becomes high logical level is measured, the value L is notobtained from Equality (1). That is, L becomes zero, which does not makesense. Therefore, when the shielding plate 202 is arranged on the sideopposite to the side of the center line of the sheet in the sheetconveying direction, only the shielding plate 202 can be detected andthe position of the side edge of a sheet cannot be measured.

Returning to the explanation of FIG. 15, the shielding plate 202 isarranged such that the end portion of the shielding plate 202 is at aposition closer to the center line of the sheet in the sheet conveyingdirection than the side edge of a sheet. At this time, as shown in FIG.16, the shielding plate 202 is arranged closer to the CIS 201 thansheet. Accordingly, it is not necessary to adjust the light intensity ofthe CIS 201 for detecting the shielding plate 202. Furthermore, with theabove configuration, when the binarization circuit 124 digitalizes theanalog output from the CIS 201, the analog output of the shielding plate202 always becomes larger than that of the sheet as long as the lightintensity is adjusted for the sheet. Therefore, the shielding plate 202can always be detected.

The operation of the CIS 201 can be checked by communication between theimage forming apparatus PR and the sheet post-processing apparatus PD.

Examples of methods for checking the operation of the CIS 201 aredescribed below.

One method is to instruct input check by the image forming apparatus PR.Upon receiving the instruction about the input check of the CIS 201 fromthe image forming apparatus PR, the sheet post-processing apparatus PDchecks the CIS 201. The sheet post-processing apparatus PD sends 0 tothe image forming apparatus PR when the CIS 201 is in an abnormal stateand sends 1 to the image forming apparatus PR when the CIS 201 in anormal state. The abnormal state can be detected based on whether theshielding plate 202 has been detected. When the CIS 201 is in theabnormal state, the image forming apparatus PR displays an error noticeon the operation panel 113 to notify the situation to users.

Another method is to perform the input check every time the sheetpost-processing apparatus PD is turned on so that a notice is sent tothe image forming apparatus PR only when the CIS 201 is in the abnormalstate. With this method, the sheet post-processing apparatus PD can benotified that the CIS 201 is in the abnormal state even when a notice isnot sent from the image forming apparatus PR.

In the above description, the examples in which the CIS 201 is used areexplained because of the assumption that the CIS 201 is employed as thelateral registration sensor 414. However, the same configuration can beattained by using other sensors such as a line sensor and a CCD sensor.

The present invention is not limited to the specific details andexamples described in the above embodiments. Accordingly, variousmodifications can be made without departing from the scope of thepresent invention.

According to the embodiment, following advantages can be obtained:

1) The mounting state and the operating state of the measuring unit (theCIS 201) can be checked without performing trial processes on a sheet.

2) The CIS 201 can perform reading control by arranging the shieldingplate 202 within a sheet conveying path.

3) Because the shielding plate 202 is arranged closer to the CIS 201than the sheet, it is not necessary to adjust the light intensity of theCIS 201.

4) Upon determining that the measuring unit (the CIS 201) is not mountedat all, an error notice can be sent to the image forming apparatus PR.

According to one aspect of the present invention, a position of the endportion of the shielding unit is measured in a measurement area, anddetermination process is performed based on a measurement result.Therefore, the setting state and the operating state of the measuringunit can be checked without performing trial processes on a sheet.

Although the invention has been described with respect to specificembodiments for a complete and clear disclosure, the appended claims arenot to be thus limited but are to be construed as embodying allmodifications and alternative constructions that may occur to oneskilled in the art that fairly fall within the basic teaching herein setforth.

1. A sheet conveying device comprising: a conveying unit that conveys asheet in a sheet conveying direction; a measuring unit that measures aposition of a side edge of the sheet in a measurement area; a shieldingunit having an end portion that is projected into the measurement areafor shielding the sheet; a first determining unit that determineswhether the shielding unit is detectable in the measurement area; and asecond determining unit that determines whether the measuring unit hasbeen mounted in the sheet conveying device based on a result obtained inthe first determining unit.
 2. The sheet conveying device according toclaim 1, wherein the measuring unit includes a plurality ofphotodetecting elements arranged in a line and along with a detectionarea corresponding to the measurement area, and the measuring unitmeasures a position of a side edge of a sheet conveyed in the detectionarea or a position of the end portion of the shielding unit based on asignal output from the photodetecting elements.
 3. The sheet conveyingdevice according to claim 2, wherein the first determining unitdetermines that the shielding unit is detectable when followinginequality is satisfied,k−α≦Q−L≦k+α where L is a value calculated by the measuring unit andrepresenting a distance from a first pixel of the photodetectingelements to the end portion of the shielding unit, k represents adistance from the end portion of the shielding unit to a last pixel ofthe photodetecting elements, α represents an assembly error of thephotodetecting elements and the shielding unit, Q represents a length ofthe detection area.
 4. The sheet conveying device according to claim 1,wherein the shielding unit is arranged at a position closer to a centerline of a sheet in the sheet conveying direction than a position of aside edge of a sheet of a minimum size that can be measured by themeasuring unit.
 5. The sheet conveying device according to claim 1,wherein a distance from the measuring unit to the shielding unit is setshorter than a distance from the measuring unit to a sheet conveyed bythe conveying unit.
 6. The sheet conveying device according to claim 1,wherein the measuring unit performs a measurement with respect to atrailing end of a sheet conveyed by the conveying unit.
 7. The sheetconveying device according to claim 2, wherein the photodetectingelement is any one of a contact image sensor, a line sensor, and acharge coupled device sensor.
 8. A punching device comprising: apunching unit that punches a sheet conveyed by the sheet conveyingdevice according to claim
 1. 9. The punching device according to claim8, further comprising an adjusting unit that adjusts a position of thepunching unit by moving the punching unit in a direction perpendicularto the sheet conveying direction based on a measurement result from themeasuring unit.
 10. A sheet processing device comprising: a processingunit that performs a predetermined processing on a sheet conveyed by thesheet conveying device according to claim
 1. 11. The sheet processingdevice according to claim 10, wherein the processing unit performs atleast one of punching, aligning, side-stitching, saddle-stitching, andcenter-folding on the sheet.
 12. An image forming apparatus comprisingthe sheet conveying device according to claim
 1. 13. An image formingapparatus comprising the punching device according to claim
 8. 14. Animage forming apparatus comprising the sheet processing device accordingto claim
 10. 15. The image forming apparatus according to claim 12,further comprising: an operation panel including a display unit, whereinwhen the second determining unit determines that the measuring unit isnot mounted, an error notice is displayed on the operation panel. 16.The image forming apparatus according to claim 13, further comprising:an operation panel including a display unit, wherein when the seconddetermining unit determines that the measuring unit is not mounted, anerror notice is displayed on the operation panel.
 17. The image formingapparatus according to claim 14, further comprising: an operation panelincluding a display unit, wherein when the second determining unitdetermines that the measuring unit is not mounted, an error notice isdisplayed on the operation panel.
 18. A method for determining whether ameasuring unit is mounted in a sheet conveying device that includes aconveying unit that conveys a sheet in a sheet conveying direction; ameasuring unit that measures a position of a side edge of the sheet in ameasurement area; and a shielding unit having an end portion that isprojected into the measurement area for shielding the sheet, wherein themethod comprising: first determining including determining whether theshielding unit is detectable in the measurement area; and seconddetermining including determining whether the measuring unit is mountedbased on a result obtained at the first determining.